A Potential Biomarker for the Onset of Psychosis in High-risk Individuals

Researchers used the auditory mismatch negativity (MMN) paradigm to evaluate its potential as a neurophysiological biomarker for psychosis.

The key to helping people living with disabling neuropsychiatric conditions such as schizophrenia is to identify, and intervene by providing suitable treatment to, individuals who are at high risk before they present with a severe psychotic episode. New findings indicate that early detection of risk in vulnerable populations may be achieved by using the auditory mismatch negativity (MMN), a measure of a well-defined, event-related potential (ERP) that is generated in response to infrequent, irregular auditory stimuli change. In other words, MMN “can be used to assess the brain's response to novel or deviant stimuli,” and, “is applied to disorder associated with disturbances in sensory information processes, including individuals with schizophrenia,” according to the authors of a study recently published in Schizophrenia Research and Treatment.

Previously published data indicate that MMN amplitudes are attenuated in patients diagnosed with schizophrenia compared with those of typical, healthy individuals. These findings also point to the fact that MMN may serve as a predictive tool, or a biomarker, of future psychosis. In the past, investigators did examine MMN amplitudes in patients at different stages of schizophrenia such as first-episode or chronic, as well as in high-risk family members of persons with schizophrenia, but the experiments provided conflicting results.

In the current study, researchers screened the participants for high risk for psychosis by using the 16-item Prodromal Questionnaire (PQ), DSM-IV, which is used to screen stage 1 of 2 for psychosis. Based on this assessment, the participants were assigned to one of two groups: if they scored between 0 and 5 they were assigned to a control condition, and if they scored a 6 or higher they were assigned to an experimental, high-risk group. If the participants self-reported having a history of a psychological or neurological condition, or if they reported having a first-degree family member with such illness, they were excluded from the analyses. With regard to the auditory MMN paradigm, the irregular (ie, deviant) tones occurred 8% of the time during the experimental procedure. Researchers positioned the electrodes at following locations: Fz, Cz, Pz, left and right mastoids, lateral and superior of the right eye, a ground electrode from the forehead, and a reference electrode from the tip of the nose.

Results indicate that, on average, at each electrode location (ie, Fz, Cz, and Pz), the participants in the high-risk group demonstrated significantly fewer negative amplitudes, compared with those in the control group of participants. Although the authors did not follow the participants over time to assess which, if any, of them experienced a psychotic episode, these data indicate that “neurophysiological correlates may also be a useful tool to accompany psychological screenings for psychosis,” they concluded.